Method and apparatus for increasing hitting efficacy in a sporting implement

ABSTRACT

A method and apparatus for increased hitting efficacy in a sporting implement. Energy absorption characteristics are adjusted so as to vary over the hitting surface of the sporting implement. This may be employed to equalize the hitting performance of the sporting implement with respect to different locations of impact thereon.

[0001] This is a continuation-in-part of Ser. No. 09/545,561, nowpending.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus forincreasing hitting efficacy in a sporting implement, particularly a golfclub.

BACKGROUND OF THE INVENTION

[0003] Many sports involve a contest regarding how far or accurately aplayer can hit a ball with a suitably adapted sporting implement. Mostsporting implements designed for hitting, e.g., baseball bats and golfclubs, have a “sweet spot” that is the best or most desirable locationfor making contact with the ball. For many sports, including golf,hitting the ball at the sweet spot results generally in the balltraveling farther and straighter than when the ball is hit at locationson the implement that are distanced from the sweet spot. As part of therationale for and fun of the sport, it takes considerable skill toconfine the point of impact with the ball to the sweet spot.Nevertheless, there has been a desire on the part of many competitors toimprove their performance by employing sporting gear that reduces thedifficulty of achieving high performance.

[0004] Aside from a potential loss of distance and control, anotherdisadvantage of the sensitivity of the performance of the hittingimplement to the location on the hitting implement that makes contactwith the ball is that the reaction is often non-linear andcounterintuitive. This may make it difficult for persons practicing thesport to interpret the reaction in such a way that allows efficientlearning.

[0005] The prior art has known golf club heads which are weighted moreheavily around their perimeters, i.e., so-called “weighted perimeter” or“cavity back” heads. These typically provide that the material of whichthe head is formed has one distinct thickness around the perimeter orperiphery of the head and another distinct thickness interior thereto,including the neighborhood of the sweet spot. Some advantage has beenclaimed in reducing the sensitivity of the head to the proximity of thelocation of a hit to the sweet spot; however, an undesirable amount ofsuch sensitivity remains.

[0006] Accordingly, there is a need for a method and apparatus forincreasing hitting efficacy in a sporting implement that minimizes oreliminates the loss of control that typically occurs when hitting atlocations thereon that are distanced from the sweet spot, and thatprovides improved feedback to the player.

SUMMARY OF THE INVENTION

[0007] The method and apparatus for increasing hitting efficacy in asporting implement of the present invention solves the aforementionedproblems and meets the aforementioned needs by providing energyabsorption characteristics that vary over the hitting surface of thesporting implement. Preferably, the characteristics are adapted so thatthe implement absorbs energy a greater amount at the sweet spot and adecreasingly lesser amount at locations that are increasingly far fromthe sweet spot. Preferably, the characteristics are adapted by providingan insert for the implement that is formed of one or more materialsproviding for a substantially uniform energy absorption property, andvarying the thickness of the insert.

[0008] Therefore, it is a principal object of the present invention toprovide a novel and improved method and apparatus for increasing hittingefficacy in a sporting implement.

[0009] It is another object of the present invention to provide a methodand apparatus for increasing hitting efficacy in a sporting implementthat minimizes or eliminates loss of control when hitting at a locationthereon that is distanced from the sweet spot of the implement.

[0010] It is yet another object of the present invention to provide amethod and apparatus for improving the feedback available to a playerusing the sporting implement.

[0011] The foregoing and other objects, features and advantages of thepresent invention will be more readily understood upon consideration ofthe following detailed description of the invention, taken inconjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a pictorial view of a sporting implement for use withthe present invention.

[0013]FIG. 2 is a pictorial view of the head of the sporting implementof FIG. 1, showing a cavity according to the present invention.

[0014]FIG. 3 is an exploded, plan view of the head of FIG. 2 taken alonga line 3-3 thereof, showing an insert for the cavity according to thepresent invention.

[0015]FIG. 4 is a pictorial view of the insert of FIG. 3.

[0016]FIG. 5 is a pictorial view of the insert of FIG. 3 covered by aselected material.

[0017]FIG. 6 is a pictorial view of an insert according to the presentinvention.

[0018]FIG. 7A is a plot of the thickness of the insert of FIG. 6 versusdistance from the sweet spot in the “+x” direction noted therein.

[0019]FIG. 7B is a plot of the thickness of the insert of FIG. 6 versusdistance from the sweet spot in the “−x” direction noted therein.

[0020]FIG. 7C is a plot of the thickness of the insert of FIG. 6 versusdistance from the sweet spot in the “+y” direction noted therein.

[0021]FIG. 7D is a plot of the thickness of the insert of FIG. 6 versusdistance from the sweet spot in the “−y” direction noted therein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0022] This invention pertains to a method and apparatus for increasinghitting efficacy in a sporting implement. A preferred, golf clubimplement for use with the invention is described below and shown inFIG. 1. However, the principles described herein apply as well to othersporting implements for use in hitting a ball or other similar objectaside from golf clubs, such as but not limited to baseball bats andhockey sticks for example.

[0023] The golf club 12 has an elongate shaft 14 and a head 16 adaptedfor hitting a golf ball (not shown). Golf clubs are provided as beingparticularly suited for specific tasks. Drivers are adapted for hittingthe ball over long distances through the air, while putters are adaptedfor hitting the ball over relatively short distances over the grass. Foreach of these purposes, the head 16 may be formed of different materialsand have different shapes. Moreover, different golf clubs having thesame purpose may be formed of different materials or have differences inshape. However, regardless of the material of which the implementgenerally or the head specifically is formed, the configuration of theimplement as a whole provides that a predetermined, relatively smallarea thereon that is the best or most desired location for hitting theball. This area is termed herein the “sweet spot,” as it is commonlyreferred to by the players engaged in sports.

[0024] The sweet spot for a golf club is somewhere on the head 16, whilethe sweet spot for a baseball bat, by comparison, is somewhere on itsbarrel. The sweet spot may have any shape or size. Referring to FIG. 1,a generalized sweet spot area 18 is indicated on a larger hittingsurface area 17 of the head 16. An area 19 of the hitting surface area17 lying outside the sweet spot 18 is a less desired location forhitting the ball than the sweet spot; however, the entire hittingsurface area 17 is adapted and intended for hitting the ball accordingto normal practice of the sport.

[0025] A problem for the player who hits the ball with the implementoutside of the sweet spot 18 yet within the hitting surface 17 is thatthe ball will typically not be as accurately or controllably directed.Moreover, the feeling that the player receives from the interaction maynot be easily interpreted to lead to appropriate corrections, makinglearning difficult. For other sports, other deleterious ramifications ofhitting the ball “off” the sweet spot may ensue.

[0026] Different heads 16 provide for unique hitting characteristicsthat vary as a function of location on the hitting surface. Toillustrate, for a given head 16 a given swing might drive the ball 10feet if the ball is hit within the sweet spot 18 for the head, while thesame swing might drive the ball only 6 feet if the ball is hit at thetoe end 20 of the head, and 8 feet if the ball is hit at the heel end 22of the head. Another head might provide for 9 feet, 6.5 feet and 8.5feet respectively at corresponding locations under the samecircumstances. These varying distances are symptomatic of theaforedescribed problems.

[0027] Turning to FIG. 2, according to the invention, a method andapparatus for increasing hitting efficacy in the golf club 12 is shown.The method and apparatus provide for equalizing the hitting distancesthat may be obtained for hitting the ball at various locations on thehead.

[0028] This equalization is performed by providing for variable energyabsorption characteristics over selected portions of the hitting surface17. This is preferably accomplished by providing a cavity 24 in the head16 that removes the surface area 17 that would otherwise be normallyused for hitting. An existing head may be machined or otherwise modifiedto include the cavity, or the head may be formed with the cavityinitially. The cavity is shown confined inside the hitting surface 17;however, it may be extended to cover the entire surface 17 and beyond(where practical) if desired.

[0029] Referring to FIG. 3, which for convenience only shows twodimensions, the cavity has a depth “e” that is a function of location onthe head. An insert 26 is installed in the cavity to restore, byproviding at least part of, the hitting surface 17 so that the hittingsurface is flat or alternatively has the shape that is normally employedfor the sport.

[0030] The insert is preferably substantially homogeneous, providing forsubstantially uniform energy absorption material properties that differ,however, from corresponding material properties of the head 16. Further,according to the invention, the insert 26 provides energy absorptioncharacteristics that vary over the hitting surface 17. These varyingcharacteristics are preferably provided by varying the thickness of theinsert at different locations on the surface 17. The thickness of theinsert is that dimension of the insert that extends normal to thehitting surface 17 as shown in FIG. 3.

[0031] Preferably, a back surface 32 of the insert 26 is complementaryto a back surface 34 of the cavity 24, i.e., the back surface 32 makesintimate contact with and follows the shape of the back surface 34. Thisprovides that the thickness of the insert is equal to the depth “e” ofthe cavity.

[0032] Employing different material properties in the insert and headpermit altering the mechanical properties of the head while retainingits original shape. The insert may be any single material or compound;however, a metal or metal matrix, or a polymer or polymer matrix arepreferred.

[0033] Providing the insert 26 with a thickness “e” that varies as afunction of location on the hitting surface 17 provides means forcontrolling the amount of energy transmitted by the head to the ball asa function of location on the hitting surface. In particular, the amountof energy transferred is controlled so as to equalize, as much as isdesired or practical in a given application (hereinafter “equalize” or“equalization”), the energy absorption characteristics of the headacross the surface 17.

[0034] To illustrate this equalization feature, a particular head 16 maynormally be used to hit the ball 10 feet at the sweet spot 18, 6 feet atthe toe end 20, and 8 feet at the heel end 22, indicating that the headis 40% less effective at hitting the ball at the toe end as comparedwith the sweet spot, and 20% less effective at the heel end than at thesweet spot. For such a head, the insert 26 may be tailored so that theresulting head/insert combination absorbs a selected maximum amount ofenergy at the sweet spot, 40% less energy at the toe end, and 20% lessenergy at the heel end. If the 40% loss at the toe end and 20% loss atthe heel cannot be achieved due to, for example, a limited depth of thecavity 24, the insert may simply be tailored to maximize energy lossesat the toe and heel, respectively.

[0035] The above analysis oversimplifies by assuming that energy losstranslates directly to distance loss, which ignores the curvature of theball's flight path and neglects the effect of air resistance. However,the principles illustrated may be used, without more, to provide for auseful improvement in hitting efficacy.

[0036] An optimized value of “e” as a function of location on thehitting surface 17 may be obtained by experiment. Alternatively, thedynamics of the interaction between the head 16 and the ball may beconsidered analytically. In that regard, it has been determined that thekinetic energy difference (ΔE) for the ball-club system before and afterimpact is expressed as: $\begin{matrix}{{\Delta \quad E} = {\frac{\alpha}{\sqrt{m}}\left( \frac{2k}{n + 1} \right)_{x_{m}}^{{3/2}\frac{3{({n + 1})}}{2}}}} & (1)\end{matrix}$

[0037] where m is the mass of the ball, x_(m) is the maximum penetrationdistance of the ball on the insert 26, and n is the exponent in theexpression F=kx^(n), which relates the force (F) exchanged between theball and the putter and the relative displacement (x) (the displacementof the insert at the point of contact). This energy differencerepresents the energy lost as a result of the impact.

[0038] The maximum penetration distance depends on the impact location,the thickness of the insert at the impact location and the shape of theinsert. Given the elastic properties of the insert material, the elasticproperties of the ball, and the change in kinetic energy with respect tothe time of initiation of impact and the time of maximum penetration,x_(m) can be calculated either semi-analytically or numerically. Ingeneral, x_(m) is inversely proportional to the thickness of the insertat the impact location. In equation (1) the constant α is such that thecoefficient of restitution for the impact e, is expressed as e=1−αu_(i)where u_(i) is the impact velocity. The coefficient of restitutionincreases with decreasing thickness of the insert at the impactlocation. The amount of increase depends on the shape of the insert andon its mechanical properties, i.e., elastic modulus and frictionalcharacteristics (energy loss from hysterisis). The mechanical propertiesof the insert influence the value of the exponent n and this togetherwith its geometrical shape dictate the coefficient of restitution as afunction of the impact location.

[0039] Based on the above, the aforementioned energy loss (ΔE) isproportional to the insert thickness raised to a power of −3(n+1)/2. Foran average value of n of 1.25, the insert thickness is thereforeapproximately proportional to ΔE³.

[0040] In the above analysis, the main body of the head 16 wasconsidered “rigid” compared to the insert. A more detailed analysis canincorporate the mass of the putter as a whole, yielding the followingexpression for the coefficient of restitution e, $\begin{matrix}{e^{2} = {1 - {\frac{2\left( {m_{1} + m_{2}} \right)}{m_{1}m_{2\quad}u_{i}^{2}}{\int{{F\left( {{x_{i}^{*}x},t} \right)}{x}}}}}} & (2)\end{matrix}$

[0041] where m₁, m₂ denote the mass of the ball and the clubrespectively, F denotes force during the impact, x is the penetrationdistance as a function of time t and an overdot denotes the timederivative. The integral in (2) can be calculated numerically. Theresults from this analysis are similar to that resulting from (1).

[0042] The aforementioned energy loss (ΔE) is preferably determinedexperimentally. In David Pelz, “Putt Like the Pros,” Harper CollinsPublishers, 1989, pp. 168, it is reported that “Energy Transfer ResultsVary with Different Designs. Impact points along center-shaftedputterfaces and heel-shafted putterfaces show differences in rolldistance for off-sweet spot strikes with each type of putter.” Pelzplots differences in roll distance for both center-shafted andheel-shafted putters for strikes at different distances away from thesweet spot along a horizontal line on the putterface. The data show thatroll distance is maximum for hits on the sweet spot, that this parameterdecreases roughly parabolically and asymmetrically about the sweet spot,much more so for a heel-shafted putter than for a center-shafted putter,and that the rate of variation is also quite different for the two typesof putters. However, since there are many factors that can influenceroll distance besides energy loss at the point of contact with the ball,it is believed the aforementioned Pelz data cannot be used to arrive atan optimum insert geometry.

[0043] The present inventors have recognized that energy loss for hitsthat vary in location along a vertical line on the putter face shouldalso vary asymmetrically and non-linearly about the sweet spot as afunction of putter geometry. The asymmetry is particularly desirable toproduce a spin on the ball.

[0044] Moreover, the insert 26 is preferably formed so that it has arelatively high energy absorption material property as compared to thatof the material of which the head 16 is otherwise formed. Accordingly,to equalize performance across the head, the thickness “e” of the insert26 should be greatest in the area of the sweet spot, where energytransfer to the ball is otherwise greatest, and should decrease as afunction of distance from the sweet spot.

[0045] Referring to FIG. 6, in accord with the principles of theinvention, an optimum insert geometry may be defined by four “quadrants”Q1, Q2, Q3 and Q4. The aforementioned hitting surface 17 lies in or isparallel to the plane “P” shown in FIG. 5 having “x” and “y” axes, theaxes representing positive and negative excursions from the sweet spot18 in orthogonal directions.

[0046] Each quadrant of the insert 26 has a thickness in the directionof a “z” axis which is orthogonal to the “x” and “y” axes. The thicknessvaries as a function of location (x, y) on the plane “P” as defined byouter surfaces S1-S4 of the respective quadrants Q1-Q4. Theintersections of various planes with the outer surfaces S1-S4 definecurvilinear lines, that are approximately ellipsoidal. In the “x-z”plane, two lines L1 and L2 are defined.

[0047] The “z” coordinate of these lines as a function of “x” representsthe thickness of the insert on the “x” axis. Similarly, in the “y-z”plane, two lines L3 and L4 are defined, where the “z” coordinate ofthese lines as a function of “y” represents the thickness of the inserton the “y” axis. Representations of the lines L1-L3 are shown in FIGS.7A-7D, respectively, illustrating some of the characteristics of theselines.

[0048] The “z” coordinate for each of these lines at the sweet spot(“x”=0 and “y”=0) is the same maximum value “R.” The lines preferablycontinuously vary curvilinearly with 15 increasing absolute values of“x” and “y.” FIGS. 3 and 4 show an insert configuration having thischaracteristic. More particularly, the thickness of the insert asrepresented by the lines L decreases curvilinearly with increasingabsolute values of “x” and “y” at an increasing rate. For example, theslope of the line L1 at the sweet spot is zero, while the slope of theline is greatest where it intersects the “x” axis.

[0049] Generally, the lines L vary asymmetrically about the sweet spot.Particularly, where the putter shaft “T” is disposed toward the quadrantdefined by the positive “x” axis and the negative “y” axis, the line L1is longer than the line L2. The inventors have also recognized that, toreduce or eliminate backspin on the ball, the line L3, representing thelower half of the insert, is longer than the line L4, representing theupper half of the insert.

[0050] The thickness of the insert can also vary stepwise, toapproximate the lines L.

[0051] Referring to FIG. 4, an insert 26 according to the presentinvention has a back surface 32 that is in general curved in threedimensions, i.e., forms a three-dimensional surface that intersects eachof three orthogonal planes at a curved line. Moreover, as mentioned, thesurface is generally asymmetric about the sweet spot. However, thesurface 32 may take simpler forms and this may be advantageous even ifgiving up some of the compensation characteristics, to reducemanufacturing costs. For example, an insert having a simpler surfacethat retains a desirable asymmetric characteristic may have a thicknessthat varies linearly with distance from the sweet spot with a slope thatvaries according to direction. In particular, such an insert that variesasymmetrically, preferably with respect to both the horizontal andvertical axes, is believed to provide a desirable “feel” that may beparticularly useful in training use by the novice golfer.

[0052] The cavity 24 may be formed in an existing head 16, or the headand cavity may be formed together. To join the insert 26 to the head,the cavity may be filled with molten material that hardens as it coolsto form the insert. The hitting surface 17 may be finished by amachining operation. The head could also be formed along with theinsert, such as by dual material injection molding. As shown in FIG. 5,the insert may be covered by any selected material 36 so that the insertis not visible. For example, the insert may be coated with an opaquecoating, or it may be covered by a thin layer of material which may bethe same material of which the insert is formed or a different material.Where a material is provided to cover the insert, this material ratherthan the insert provides at least part of the hitting surface 17.

[0053] It is further believed that golf clubs in particular, asdistinguished from most other hitting implements used in sports, arebest used in the manner of pendulums, meaning that the weight of thehead and not any manipulation of the shaft by the player's fingers orhands, is of primary importance to properly hitting the ball.Accordingly, it is desirable where changing the weight of the head 17 byuse of the insert 22, to add or subtract mass from the head to adjustthe weight to a desired or original amount. This is often achievablewithout changing substantially the exterior dimensions of the head.

[0054] It is to be recognized that, while a particular method andapparatus for increasing hitting efficacy in a sporting implement hasbeen shown and described as preferred, other configurations and methodscould be utilized, in addition to those already mentioned, withoutdeparting from the principles of the invention. For example, the insertcould be provided so that it does not maintain intimate contact with thecavity. This would impact many of the considerations discussed above inconnection with the preferred embodiment but would not depart from theprinciples of the invention.

[0055] The terms and expressions which have been employed in theforegoing specification are used therein as terms of description and notof limitation, and there is no intention of the use of such terms andexpressions of excluding equivalents of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

1. A golf club head for hitting a golf ball comprising a body portionand an insert portion contained in said body portion that is relativelyenergy absorbing as compared to said body portion, said insert having athickness which is defined by a maximum value and which decreasestherefrom at an increasing rate with increasing distance in at least thetwo opposite directions defined by a first axis.
 2. The golf club headof claim 1, wherein said thickness decreases from said maximum value atan increasing rate with increasing distance in at least the twoadditional opposite directions defined by a second axis that isperpendicular to said first axis.
 3. The golf club head of claim 2,wherein said thickness decreases from said maximum value at anincreasing rate with increasing distance in all directions.
 4. The golfclub head of claim 1, wherein said thickness decreases asymmetricallywith respect to said two opposite directions.
 5. The golf club head ofclaim 2, wherein said thickness decreases asymmetrically with respect tothe two opposite directions defined by said first axis.
 6. The golf clubhead of claim 2, wherein said thickness decreases asymmetrically withrespect to the two opposite directions defined by said second axis. 7.The golf club head of claim 3, wherein said thickness decreasesasymmetrically with respect to any two opposite directions.
 8. The golfclub head of claim 1, wherein said insert has a front surface that formsat least part of a hitting surface adapted for making intimate physicalcontact with the golf ball.
 9. The golf club head of claim 1, whereinsaid insert has a front surface that is spaced from a hitting surfacethat is adapted for making intimate physical contact with the golf ball.10. A golf club head for hitting a golf ball comprising a body portionand an insert portion contained in said body portion that is relativelyenergy absorbing as compared to said body portion, said insert portionhaving a thickness which is defined by a maximum value and whichdecreases linearly from said maximum value with increasing distanceasymmetrically with respect to at least the two opposite directionsdefined by a first axis.
 11. The golf club head of claim 10, whereinsaid thickness decreases linearly from said maximum value withincreasing distance in at least the two additional opposite directionsdefined by a second axis that is perpendicular to said first axis. 12.The golf club head of claim 11, wherein said thickness decreaseslinearly from said maximum value with increasing distance asymmetricallywith respect to the two opposite directions defined by said second axis.